The invention relates to automatic valves for priming sewer line drain traps.
Sewer line drain traps are provided to prevent escape of gas from sewer lines. Typically, an elbow is provided in the sewer line adjacent to a drain, and the elbow is filled with water to prevent flow of gas from the sewer through the elbow. It is well recognized that water in the trap will evaporate over time, thus adversely affecting operation of the trap, so it is important that the trap be charged periodically to maintain the required level of water.
It is desirable that the sewer trap be charged with water automatically. However, such a system typically requires a connection between the sewer drain trap and a source of water, which creates a potential for contamination of the water source by siphoning of sewer water should there be a loss of water supply pressure. Sullivan U.S Pat. No. 4,204,556 sought to address this concern with an automatic primer valve having a case defining an intermediate supply chamber for water to be delivered to the sewer trap in which the biasing force for charging water into the intermediate supply chamber is a volume of air trapped within the upper portion of that chamber. Mosbrucker et al. U.S. Pat. No. 4,497,337 describes a primer valve in which the biasing force for charging water into the sewer trap is a volume of air trapped below a sliding piston.